1. Field of the Invention
The present invention relates to a communication apparatus that handles communications utilizing impulses.
2. Description of the Related Art
Recently, attention has been drawn to ultra wideband (UWB) communications. The USB communications may be categorized into communications in which the carrier is modulated by DD-SS (Direct Sequence Spectrum Spread) and communications in which impulses are directly sent and received without any carrier. The former type of communications is disclosed in Japanese Patent Publication No. 7-44514 (Document 1), and the latter type is disclosed in Japanese Patent Application Publication No. 8-509110 (Document 2).
The DD-SS type communications need a spreading code at both the transmission and reception sides. The spreading code is used for spreading at the transmission side and for dispreading at the reception side. In addition, the reception side is required to perform acquisition and tracking of synchronization. Thus, the DD-SS type communications need complicated structures and sequences.
In contrast, the communications in which impulses are directly sent and received do not need spreading and dispreading, but requires the reception side to be synchronized with the transmission side. For this requirement, the transmitter generates and sends a pulse for synchronization (synchronous pulse) to the receiver, which receives the synchronous pulse and establishes synchronization with the transmitter. For example, a radar apparatus shown in FIGS. 20 and 21 disclosed in Document 2 function as a receiver required to utilize the received synchronous pulse for establishing synchronization with the transmitter. However, there is a difficulty in establishment of synchronization between the transmitter and the receiver, particularly when the period of impulses is relatively short. Thus, even the communications in which the impulses are directly sent and received need complicated structures and sequences like the DD-SS type communications.